1. Field of the Invention
The present invention relates to a member for regulating the quantity of a developer for use to develop an electrostatic latent image formed on an image carrying member so as to form a visible image, and also to a developing unit using the member for regulating the quantity of a developer.
2. Related Background Art
A developing unit, as shown in FIG. 2, comprises a developer carrying member 3 (hereinafter a "developing sleeve") attached to a developer container 2 and disposed at a predetermined distance from the electrophotographic photosensitive member 1; a blade 4 (hereinafter an "elastic blade") for regulating the quantity of the developer; an elastic roller 5; and a one-component developer 6 (hereinafter "toner"). As a means for reducing the thickness of a toner layer, which is carried by the developing sleeve to the developing portion, a structure has been known in which the elastic blade 4 is brought into contact with the developing sleeve to regulate the toner, which is allowed to pass through a nip formed between the elastic blade 4 and the developing sleeve 3, to form a thin layer of toner on the developing sleeve 3; and a frictionally generated electric charge (triboelectricity) for forming a latent image is supplied to the toner 6 in the contact portion between the elastic blade 4 and the developing sleeve 3.
Since distribution of the size of toner particles ranges from several microns to tens of microns in the toner layer formed on the developing sleeve 3, the development process using the elastic blade 4 is required to accurately bring the elastic blade 4 to the top end of the surface of the developing sleeve, to frictionally generate an electrical charge to the toner 6 held between the developing sleeve 3 and the elastic blade and to form a uniform thin layer on the developing sleeve 3.
Referring now to FIGS. 1A and B as an elastic blade 4 for regulating the quantity of the developer 6, a rubber member 14 or a member 7 manufactured by integrating a supporting member 7a made of metal foil or a plastic sheet and a rubber member 7b has been used. As the rubber member, a urethane rubber elastic member for regulating the quantity of a developer has been used.
As the urethane rubber member, adipate urethane rubber containing polyester polyol as the molecular skeleton thereof has been mainly used for the purposes of wear resistance, low plasticity deformability and ease of frictional electricity charging.
However, a hydrolyzing reaction proceeds in the member for regulating the quantity of a developer using urethane rubber as time passes due to water in the air, causing the physical properties to deteriorate. Such deterioration leads to a fact that the pressure of the member for regulating the quantity of a developer to press the developing sleeve is lowered and, therefore, the set pressure level is changed undesirably or the area of contact is changed due to the deterioration in the hardness of the rubber. Thus, the ease in forming the thin layer and frictionally with electricity deteriorates.
An apparatus for developing an electrostatic latent image formed on the image carrying member to obtain a visible image, for example, a copying machine or a laser beam printer, encounters excessive rise in the temperature therein to about 40.degree. C. and lowering in the temperature to the ambient temperature after the operation of the apparatus has been stopped. Therefore, dew condensation takes place repeatedly by a degree corresponding to the ambient humidity while subjecting the urethane elastic blade to a similar condition. Thus, the quality of the developed image is affected considerably by the deterioration occurring due to hydrolyzing reaction caused from the contact with water taking place in accordance with the temperature, humidity and the period of use.
In particular, the adipate urethane rubber containing polyester polyol as the molecular skeleton thereof has excellent characteristics exemplified by the wear resistance as compared with polyether polyol. However, the adipate urethane rubber containing the ester group that has poor resistance against hydrolysis encounters change in the molecular structure of urethane rubber, causing its initial mechanical characteristics to deteriorate such that the mechanical characteristics deteriorates rapidly in an exponential function manner due to factors, such as time, temperature and humidity. As a result, use of the adipate urethane rubber for a long time under a certain environment causes the hardness of the rubber to be changed and plastic deformation to take place due to deterioration in the mechanical characteristics. Thus, the reduction in the contact pressure with the developing sleeve deteriorates the ease in forming a thin layer and frictionally charging the toner. What is worse, the deterioration further increases the viscosity of the rubber, causing a problem to occur in that the rubber adheres to the developing sleeve or the toner.
Accordingly, suggestions have been made to use a hydrolysis prevention material capable of preventing hydrolysis of the urethane rubber and to use an anti-oxidant to prevent deterioration in the urethane rubber due to heat.
However, a desire for reducing the cost of the elastic blade made of urethane rubber and improving manufacturing yield raises the necessity of improving the urethane moldability and, thus, a catalyst capable of enhancing the reaction must be used in a considerably large quantity. The catalyst undesirably enhances the hydrolysis, thus causing a problem in that satisfactory quality cannot be obtained and the period, in which the urethane blade can be used, cannot be lengthened.